Density functional calculation of N-N barrier and analysis of vibrational spectra for nitrosoisocyanate and nitroisocyanate

The structural stability of nitro ioisocyanate O=C=N-NO and nitroisocyanate O=C=N-NO2 were investigated using ab initio calculations. The calculations were carried out at DFT-B3LYP/6-311++G** level. From the calculation nitrosoisocyanate was predicted to exist predominantly in the trans conformation with high trans-cis rotational barrier. The rotational barrier of the NO group was calculated to be about 6 kcal/mol, while that of the NO2 group to be of about 2 kcal/mol. The vibrational frequencies were computed, normal coordinate calculations were carried out and potential energy distributions were calculated for both molecule:. A complete vibrational assignment was provided for the normal modes of the two molecules. (C) 2001 Elsevier Science B.V. All rights reserved.